Ten phenolic compounds, isofraxidin (1), (+)-syringaresinol-di-O-beta-D-glucoside (2), syringin (3), chlorogenic acid (4), isofraxidin-7-O-beta-D-glucoside (5), 2,6-dimethoxy-p-benzoquinone (6), (+)-pinoresinol-O-beta-D-glucoside (7), (7), (+)-syringaresinol-O-beta-D-glucoside (8), (+)-pinoresinol-di-O-beta-D-glucoside (9) and (+)-medioresinol-di-O-beta-D-glucoside (10), were isolated from the stem bark of Acanthopanax senticosus Harms and identified, respectively. The aqueous extract of the stem bark exhibited a prolonging effect on the exercise time to exhaustion in chronic swimming stressed rats. The effect on the exercise time in the chronic swimming stressed rats was respectively tested for compounds 2 and 4, which are major constituents of the stem bark. As a result, it was indicated that compound 2 is the compound responsible for part of the pharmacological effect which the aqueous extract of the stem bark showed.